Mobile communication devices typified by smartphones and mobile phones have been sophisticated. For example, the transition from 3G systems to LTE (Long Term Evolution) has rapidly progressed. In LTE, a single terminal needs to support a large number of frequency bands.
International Publication Nos. 2013/073472 and 2012/114930 and Japanese Patent Application Publication Nos. 2014-502803 and 2004-072549 (Patent Documents 1 through 4) disclose filters capable of changing the frequency and the bandwidth. U.S. Pat. No. 3,831,116 (Patent Document 5) discloses a filter in which a switch is located in an Interdigital Transducer (IDT).
The techniques disclosed in Patent Documents 1 through 4 change the frequency characteristics of the filter by adding an electrostatic capacitance in series or parallel to a resonator. However, the addition of the electrostatic capacitance changes the impedance characteristic.